Kinesins are motor proteins that use adenosine triphosphate to bind to microtubules and generate mechanical force. Kinesins are characterized by a motor domain having about 350 amino acid residues. The crystal structures of several kinesin motor domains have been resolved.
Currently, about one hundred kinesin-related proteins (KRP) have been identified. Kinesins are involved in a variety of cell biological processes including transport of organelles and vesicles, and maintenance of the endoplasmatic reticulum. Several KRPs interact with the microtubules of the mitotic spindle or with the chromosomes directly, and appear to play a pivotal role during the mitotic stages of the cell cycle. These mitotic KRPs are of particular interest for the development of cancer therapeutics.
Eg5 (also known as HsEg5, KNSL1, or KSP) is one of several kinesin-like motor proteins that are localized to the mitotic spindle and known to be required for formation and/or function of the bipolar mitotic spindle.
In 1995, the depletion of Eg5 using an antibody directed against the C-terminus of Eg5 was shown to arrest HeLa cells in mitosis with monoastral microtubule arrays (Blangy et al., Cell 83:1159-1169, 1995). Mutations in bimC and cut7 genes, which are considered to be homologues of Eg5, cause failure in centrosome separation in Aspergillus nidulans (Enos, A. P., and N. R. Morris, Cell 60:1019-1027, 1990) and Schizosaccharomyces pombe (Hagan, I., and M. Yanagida, Nature 347:563-566, 1990). Treatment of cells with either ATRA (all trans-retinoic acid), which reduces HsEg5 expression on protein level, or depletion of HsEg5 using antisense oligonucleotides revealed a significant growth inhibition in DAN-G pancreatic carcinoma cells indicating that HsEg5 might be involved in the antiproliferative action of all trans-retinoic acid (Kaiser, A., et al., J. Biol. Chem. 274, 18925-18931, 1999). Interestingly, the Xenopus laevis Aurora-related protein kinase pEg2 was shown to associate and phosphorylate X1Eg5 (Giet, R., et al., J. Biol. Chem. 274:15005-15013, 1999). Potential substrates of Aurora-related kinases are of particular interest for cancer drug development. For example, Aurora 1 and 2 kinases are overexpressed on protein and RNA level and the genes are amplified in colon cancer patients.
The first cell permeable small molecule inhibitor for HsEg5, “monastrol”, was shown to arrest cells with monopolar spindles without affecting microtubule polymerization as do conventional chemotherapeutics such as taxanes and vinca alkaloids (Mayer, T. U., et al., Science 286:971-974, 1999). Monastrol was identified as an inhibitor in phenotype-based screens and it was suggested that this compound may serve as a lead for the development of anticancer drugs. The inhibition was determined not to be competitive in respect to adenosine triphosphate and to be rapidly reversible (DeBonis, S., et al., Biochemistry 42:338-349, 2003; Kapoor, T. M., et al., J. Cell Biol. 150:975-988, 2000).
Recently, other Eg5 kinesin inhibitors have been described. WO 02/057244 and WO 02/056880 describe phenothiazine compounds and triphenylmethane compounds, respectively, for treating proliferative diseases. WO 02/078639 describes cyano-substituted dihydropyrimidine compounds for treating proliferative diseases. U.S. Pat. No. 6,472,521 describes oligonucleotides and oligonucleotide derivatives for inhibiting human Eg5 expression.
WO 01/98278, WO 01/30768, and WO 03/039460 describe quinazolinone compounds that are useful in treating cellular proliferative diseases associated with KSP kinesin activity. The compounds described in these references are 22-aminomethyl)quinazolinone derivatives. The quinazolinone compounds described in WO 01/98278 and WO 01/30768 have 2-aminomethyl substituents that are either amine, amide, or sulfonamide substituents. The quinazolinone compounds described in WO 03/039460 have the amino group of the 2-aminomethyl substituent incorporated into a 5-12 membered nitrogen-containing heterocycle.
A crystal structure of Eg5 bound to ADP-Mg was recently determined (J. Biol. Chem., Vol. 276, No. 27, pp. 25496-25502). However, this crystal structure does not provide information with respect to the manner in which inhibitors bind Eg5. Consequently, the design of Eg5 inhibitors can be greatly facilitated if a crystal structure of an inhibitor complexed to Eg5 were to be determined.
Recently, a crystal structure of Eg5 bound to Eg 5 ligands was published (WO 2004/004652. This publication identified a binding pocket of Eg5. Nevertheless, there is a need to identify an Eg5 binding pocket that differs from the binding pocket disclosed in WO 2004/004652.